Process of preparing salt-free n-acyl taurines



United States Patent PROCESS OF PREPARING SALT-FREE N-ACY L TAURINES Fred 'J. Gajewsiri, Westfield, and Leslie M. Schenck, Mountainside, N.J., assignors to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 30, 1958, Ser. No. 783,680

16 Claims. (Cl. 260--401) This invention relates to an improved process for preparing salt-free N-acyl taurines and more particularly, to an improved process for separating such taurines from aqueous slurries containing both water'soluble salts and such taurines.

The reaction of higher fatty acids, fatty acid chlorides and fatty acid esters with Z-aminoalkane sulfonic acids (taurines) and the alkali metal salts thereof to yield anionic surface active materials useful as wetting, cleansing, softening and dispersing agents is well known. In US. Patent No. 1,932,180, several processes are described for the preparation of such surface active materials, but the only process which has up to the present been employed commercially is that wherein an acid chloride is reacted in aqueous medium with a 2-aminoalkane sulfonic acid in the presence of an acid neutralizer such as caustic soda. This inherently produces, in addition to the N-higher acyl taurine, a considerable quantity of salt, e. g. sodium chloride (or potassium chloride if caustic potash is used as acid neutralizer) as a by product.

The presence of such salts with the N-higher acyl taurine is highly undesirable and disadvantageous for a number of reasons. Not only do such salts have a substantial corrosive eifect in the packaging and handling of detergents and other surface active compositions containing such acyl taurines, but they also exert a strong adverse effect on the lathering, detergent and other surface active properties of mixtures of such acyl taurines with soap. The acyl taurines are very goodlime soap dispersants and the combination or" minor amounts thereof with ordinary fatty acid soaps in detergent and built soap formulations results in highly effective detergent properties, particularly in hard water. However, for such combinations to have optimum properties, the N- higher acyl taurine present thereinshould have a low salt content.

The presence of this salt in a number of commercially available N-acyl' taurines has been identified as a major reason for the unduly high hygroscopicity of such products. The presence of such salt is also undesirable when the N-acyl taurine is to be employed in certain emulsion polymerization reactions and in other uses.

A. number of proposals have been made in the prior art for the production of salt-free N-higher acyl taurines, some of which involve the use of a different method of reaction or of different reactants in the production of such taurines, and others of which involve expensive and diflicult separation methods.

it is an object of this invention to provide a process for producing a salt-free N-higher acyl taurine which will not be subject to the above disadvantages. Another object of this invention is the provision of a process for producing a salt-tree N-higher acyl taurine from an aqueous slurry containing such taurine in combination with a water soluble salt. Other objects and advantages will appear as the description proceeds.

The attainment of the above objects is made possible by the present invention which includes a process comprising intimately mixing an aqueous slurry containing (A) an N-higher acyl taurine of the formula wherein one R is selected from the group consisting of H and methyl and the other R is H, R is selected from the group consisting of H and hydrocarbon radicals of l to 6 carbon atoms, R is selected from the group consisting of aliphatic, alicyclic and aromatic hydrocarbon radicals of 7 to 23 carbon atoms, and M is selected from the group consisting of l-I, alkali metal, alkaline earth metal, ammonium and amino, and (B) a water soluble salt selected from the group consisting of the alkali metal chlorides and sulfates, with a water insoluble compound (C) selected from the group consisting of aliphatic and alicyclic monocarboxylic acids of 8 to 24 carbon atoms and their esters in an amount and at a temperature sufiieient to form a compatible liquid solvent system with said taurine (A), allowing the resulting mixture to settle into a lower aqueous phase and an upper oil phase containing said solvent system, and then separating said aqueous phase from said oil phase at a temperature above the solidification point of said solvent system.

An outstanding advantage of the process of this invention is thatit is operable on the commercially available N-higher acyl taurines produced by the Schotten- Baumann reaction between a higher fatty acid chloride and a taurine, and may be carried out by soap manufacturers themselves in readily available equipment. The product produced by the above process is a mixture of the acyl taurine with the higher molecular weight carboxylic acid or ester which may be employed as such in certain cosmetic and other uses, or may be treated with an inorganic or organic base such as the alkali metals or amines such as triethanolamine or the like to saponify the carboxylic acid and produce its soap in situ. Such soap compositions are useful directly as toilet soaps and other cosmetic applications in liquid or solid form and can readily be formulated into bars or cakes. If desired, the resulting combination of soap and N- higher acyl taurine may be spray dried or drain dried to produce a flake or powder detergent and may be combined before or after such drying with common builders, stabilizers and the like for the production of heavy duty built detergent compositions. Common components of such built compositions include alkali metal phosphates and poly-phosphates, silicates, carbonates, and sodium carboxymethyl cellulose. I

Since the present process is performed at. moderate temperatures, no discoloration of product or reactants is experienced and the original purity of the intermediates is representative of the final product, excluding these impurities that are removed during the processing. Highly specialized equipment required by the prior art to maintain the necessary reaction conditions for the production of the desired salt-free N-higher acyl taurines is no longer necessary. The operability of the, present process is surprising and unexpected in view of the anticipated emulsification and/or foaming which would normally be expected to occur in a fatty acid-synthetic detergent-soap and water formulation of the. type involved in the present process.-

If a final product is desired which must be not only salt-free but also substantially pure, the higher carboxylic acid employed to form a compatible solvent system with the acyl taurine maybe conveniently removed by asubsequent distillation.

The process of this invention is applicable for the treatment of any aqueousslurry containing theN-higlier j are produced in salt-free form in accordance with this invention may in general be ascribed the formula given above. Such acylated taurines may be prepared by reaction of a taurine salt containing at least one N- bonded hydrogen atom with a higher molecular weight acylating agent of the formula RCOOH or R'COCl. Those acylating agents particularly preferred are the higher free fatty acids of 12 to 18 carbon atoms (R is 7 to 17 carbon atoms). As generally representative of higher aliphatic and alicyclic carboxylic acids operative in the instant invention, there may be mentioned caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, ricinoleic acid, linoleic acid, undecylenic acid, tall oil acid, acid mixtures from various natural plant and animal oils such as olive, tallow, castor, peanut, coconut, soybean, cotton seed, ucuhuba, linseed, cod, herring, menhaden, neats-foot, sperm, palm, corn, butter, babassu, kapok, hempseed, mustard, rubberseed, rape, sunflower, sesame, acids from the oxidation fractions of petroleum, and from oxo-aldehydes, naphthenic acids, abietic acids, and the hydrogenated derivatives of such acids and acid mixtures. Other acids which may be employed include alkyl benzoic acids such as dodecyl benzoic acid, nonyl benzoic acid, octyl benzoic acid, alkyl naphthoic acids such as nonyl naphthoic acid, and the like.

The above described carboxylic acid acylating agents are accordingly representative of the aliphatic, alicyclic and aromatic hydrocarbon radicals of 7 to 23 carbon atoms which may be employed as R in the above formula. Such carboxylic acid acylating agents (eg RCOCl) are reacted with taurines of the formula HRN-CHR--CHRSO M to produce the acylated taurines treated in accordance with the present process. In this formula, R may represent hydrogen, methyl, ethyl, isopropyl, butyl, hexyl, cyclohexy'l, phenyl and the like, and M may represent hydrogen or a salt-forming cation such as an alkali metal, e.g. sodium, potassium or lithium, an alkaline earth metal such as calcium, mag- .nesium or barium, ammonium, or an amine such as mono-, dior tri-ethanolamine, cyclohexylamine, guanidine or the like. Thus, by way of example, only the following specific Z-aminoalkane sulfonic acids may be employed as such or in the form of their salts for reaction with the above defined carboxylic acid acylating agents: taurine, N-methyl taurine, N-ethyl taurine, N-propyl taurinefi N-isopropyl taurine, N-butyl taurine, N-amyl taurine, N-hexyl taurine, N-cyclohexyl taurine, N-phenyl taurine, N-methyl-Z-methyl taurine, N-methyl-l-methyl taurine, and the like.

The aqueous slurries treated in accordance with the present process should in general be sufficiently fluid to be readily workable. In general, in such slurries, the acylated taurine would be present in concentrations of about to 40% by weight, 35% slurries being those most readily available on the market. In such slurries, the water soluble salts usually present as a result of the method manufacturing the acylated taurine may be present in proportions as high as 30 to 35 of the weight of the acylated taurine, to being common. It will of course be understood that the present process is also operative for removing smaller proportions of salt, e.g. as little as 5% or less or higher proportions, e.g. up to 50% or more, of the weight of the acylated taurine. The salt most commonly present in such slurries is sodium chloride, usually accompanied bysmaller proportions of sodium sulfate. However, potassium chloride and potassium sulfate may also be present for other reasons or because potash was employed in the reaction for producing the acylated taurine. The acylated taurine slurries commonly available normally have a pH of about 7 to-8, but the process of this invention is operative not only on these slurries but on those of a much higher acidity or alkalinity.

As stated above, the process of this invention requires the intimate admixture of an aqueous slurry as above described with a water insoluble compound (component C) selected from the group consisting of aliphatic and alicyclic monocarboxylic acids of 8 to 24 carbon atoms and their esters in an amount and at a temperature sufiicient to form a compatible liquid solvent system with the acylated taurine (component A). The preferred component C for use in the present process is a free higher fatty acid of 12 to 18 carbon atoms which may be saturated or unsaturated, branched but preferably straight. Other aliphatic and alicyclic monocarboxylic acids which may be employed as component C in the present process include those disclosed above as operative acylating agents (RCOOH) with the exception of the alkyl benzoic and alkyl naphthoic acids since component C and component A (acylated taurine) must be mutually soluble to form a compatible solvent system liquid under the conditions of the intimate admixture required in the present process. The methyl, ethyl, propyl or glyceryl esters of such acids may also be employed. It will be generally found that the amount of component C necessary to form a compatible liquid solvent system with component A at the temperature of separation of the aqueous and oil phases in the mixture above the solidification point of such system will be at least twice the weight of said component A (acylated turine), and will in general range from about 2 to 12 parts, preferably 2.5 to 7 parts, per part by weight of component A. Higher proportions may be employed but are uneconomical except where a larger proportion of soap is desired in the final product as obtained by saponification of component C in situ following removal of the aqueous phase in accordance with the present process.

After addition of the required amount of component C to the aqueous slurry containing the acylated taurine and water soluble salt, the resulting mixture is subjected to agitation for a sufiicient length of time to allow intimate admixture of the acylated taurine with component C and consequent formation of the aforesaid compatible liquid solvent system, camponents A and C being mutually soluble. The duration of agitation for achieving optimum results regarding formation of an oil phase containing components A and C and an aqueous phase containing most of component B will be in any particular instance readily determinable by routine experimentation, and will, in most instances, range from about 10 minutes to '2 hours, about /2 to 1 hour being usually sufficient. During this agitation, the temperature of the mixture should obviously be maintained at a temperature sufiicient to maintain the mixture in liquid condition, i.e. above the solidification point of the compatible solvent system containing components A and C and below the boiling point of the mixture, The preferred range is about 60 to C. in order to maintain the mixture in as fluid a condition as possible while avoiding difficulties due to foaming, etc., at temperatures approaching the boiling point of the water in the mixture under the conditions involved. Higher temperatures may of course be employed of up to about C. if the agitation is carried out under pressure to avoid boiling, but temperatures above about 200 C. are preferably avoided to prevent discoloration and/or decomposition of the acylated taurine.

To facilitate a more rapid and complete subsequent separation of the oil and aqueous phases in the mixture, an additional amount of water-soluble inorganic salt (preferably alkali metal chloride or sulfate) may be added during this agitation step. Such addition usually takes the form of a saturated aqueous solution of the salt in an amount by volume which may be less than, more than, or, usually, equal to the volume of the initial aqueous slurry containing the acylated taurine and salt.

Following completion of this agitation step, the mixture is allowed to stand at similar temperatures for a suflicient length of time to permit optimum separation of B from the upper oil phase containing components'A and C. This duration will likewise be readily ascertainable by routine experimentation in any particular instance, generally ranging from about 5 to 25 hours and usually from about to 2 0 hours. Following this settling period, the phases may be readily separated from each other at similar temperatures in known manner, e.g. decantation, siphoning, pumping, centrifuging, membrane separation, etc.

By the present process, there is thus obtained from the original aqueous slurry a substantially homogeneous mixture or solution of component A and component C. This product is advantageously subjected to saponification with caustic soda or potash to produce the soap of component C in situ together with the acylated taurine. However, if desired, component C may be separated from the acylated taurine by distillation or the like.

The following examples, in which parts are by weight,

unless otherwise indicated, are only illustrative of the instant invention and are not to be regarded as limitative. In these examples, all parts and proportions of fatty acid amides are determined by the methylene blue analytical method described in Nature 160, 759 (1947) and Trans. Faraday Soc. 44, 226-239 (1948). The talloW fatty acid contains, by weight, approximately 10% myristic, 43% palmitic, 9% stearic, 30% oleic, and 8% linoleic acids, and the coconut fatty acid contains, approximately, 8% caprylic, 7% capric, 49% lauric, 17% myristic, 9% palmitic, 2% stearic, 6% oleic, and 2% linoleic acids.

Example 1 Three hundred grams of a commercial aqueous slurry containing by weight 75 g. of sodium-N-methyl-N-coconut fatty acid taurate and 17.25 g. sodium chloride is admixed with 200 g. tallow fatty acid and heated at 95 C. with agitation for one hour. The mixture is allowed to stand 18 hours at 90 to 95 C., and the lower aqueous phase separated from the oil layer.

Upon analysis, the oil layer is found to contain 200 g. tallow fatty acid, 74.5 g. of said taurate, 4.82 g. sodium chloride and 94 g. of water. By the extraction, 72% of the salt originally present in the commercial slurry is removed in the aqueous layer Upon conversion of the fatty acid in the oil layer to a partial sodium soap by saponification with caustic in situ, a free lathering soap bar is produced containing of said taurate by weight.

Example 2 Two hundred twenty seven grams of a commercial aqueous slurry containing 75 g. oleoyl taurate and 17 g. sodium chloride is agitated one hour at 100 C. with 300 g. oleic acid. The mixture is then allowed to stand 2 hours at 100 C. and 14 hours at 75 C. The clear aqueous layer (95.5 g.) is separated and found to contain 14.8 g. sodium chloride and no taurate. The oil layer, 421 g., contains 75 g. of said taurate and 2.2 g. sodium chloride in addition to the oleic acid.

Example 3 One hundred and fifty grams of a commercial slurry containing 28.4 g. sodium-N-cyclohexyl-N-palmitoyl taurate and 6.82 g. salt is treated with 200 g. commercial oleic acid in the manner described in Example 2. The oil layer is found to contain 28.0 g. of said taurate, and 0.42 g. of salt, in addition to the oleic acid.

Example 4 Five hundred grams of a commercial aqueous slurry containing 96.7 g. of sodium-N-methyl-N-stearoyl taurate and 20.8 g. of sodium chloride is admixed with 500 g. saturated salt (sodium chloride) Water and 1000 g. double pressed stearic acid. The slurry is heated to 95 C.

sodium-N-methyl-N- and cyclohexyl, R is selected from the group consisting over a hour period with agitation, then allowed to stand at C. for twenty hours. The separated oil layer contains, in addition to the stearic acid, 96.3 g. of said taurate and 0.415 g. sodium chloride, 2. reduction of 98% in salt content.

Example 5 Nine hundred grams of a commercial aqueous slurry containing 225 g. of sodium-W-methyl-N coconut fatty acid taurate and 51.75 g. of sodium chloride is agitated at 90 C. for A2 hour with 600 g. coconut fatty acid and 900 g. saturated sodium chloride solution. The mixture is allowed to stand 20 hours at 94 C., and the aqueous layer withdrawn. The oil layer contains 224 g. of said taurate and 12 g. of sodium chloride in addition to the coconut fatty acid.

Example 6 The procedure of Example 5 is repeated, except that the temperature of agitation is 70 C. and 900 g. of methyl oleate is employed instead ofthe 600 g. of coconut fatty acid. Similar recovery results are obtained' Example 7 Example 8 The procedure of Example 1 is repeated except that the taurate in the initial slurry is s0diun1-Nmethyl-N- tallow fatty acid taurate. Similar results are obtained.

This invention has been disclosed with respect to certain preferred embodiments, and various modifications and variations thereof will become obvious to the person skilled in the art. It is to be understood that such modifications and variations are to be included within the spirit and purview of this application and the scope of the appended claims.

We claim:

1. A process comprising intimately mixing an aqueous slurry containing (A) an N-higher acyl taurine of the formula R'CONR-CHRCHRSO M wherein one R is selected from the group consisting of H and methyl and the other R is H, R is selected from the group consisting of H, phenyl, alkyl radicals of 1 to 6 carbon atoms,

of aliphatic and alicyclic hydrocarbon radicals of 7 to,23 carbon atoms, and M is selected from the group consisting of H, alkali metal, alkaline earth metal, ammonium and amino, and (B) a water soluble salt selected from the group consisting of the alkali metal chlorides and sulfates, with a water insoluble compound (C) selected from the group consisting of aliphatic. and alicyclic monocarboxylic acids of 8 to 24 carbon atoms and their esters in an amount and at a temperature sufilcient to form a compatible liquid solvent system with said taurine (A), allowing the resulting mixture to settle into a lower aqueous phase and an upper oil phase containing said solvent system, and then separating said aqueous phase from said oil phase at a temperature above the solidification point of said solvent system.

2. A process as defined in claim 1 wherein component A is sodium-N-methyl-N-"coconut fatty acid taurate.

3. A process as defined in claim 1 wherein component A is sodium N-methyl-N-tallow fatty acid taurate.

4. A process as defined in claim 1 wherein component A is sodium-N-oleoyl taurate.

5. A process as defined in claim 1 wherein component A is sodium-N-cyclohexyl-N-palmitoyl taurate.

6. A process as defined in claim 1 wherein component A is sodium-N-methyl-N-stearoyl taurate.

7. A process as defined in claim 1 wherein component C is a free fatty acid of 12 to 18 carbon atoms.

8. A process as defined in claim 1 wherein said component C is admixed with said slurry in an amount at least twice the weight of said component A.

9. A process comprising intimately admixing an aqueous slurry containing an N-higher fatty acid taurine compound and an alkali metal chloride with an amount of higher fatty acid of 12 to 18 carbon atoms and a temperature sufficient to form a compatible liquid solvent system with the said taurine compound, allowing the resulting mixture to settle into a lower aqueous phase and an upper oil phase containing said solvent system, and then separating said aqueous phase from said oil phase at a temperature above the solidification point of said solvent system.

10. A process as defined in claim 9 wherein said higher fatty acid of 12 to 18 carbon atoms is coconut fatty acid.

11. A process as defined in claim 9 wherein said higher fatty acid of 12 to 18 carbon atoms is tallow fatty acid.

12. A process as defined in claim 9 wherein said higher fatty acid of 12 to 18 carbon atoms is palmitic acid.

13. A process as defined in claim 9 wherein said higher fatty acid of 12 to 18 carbon atoms is oleic acid.

14. A process as defined in claim 9 wherein said higher fatty acid of 12 to 18 carbon atoms is stearic acid.

15. A process as defined in claim 9 wherein said higher fatty acid of 12 to 18 carbon atoms is coconut oil.

16. A process as defined in claim 9 wherein said higher fatty acid is admixed with said slurry in an amount ranging from about 2 to 12 parts by weight per part of the said taurine compound in the slurry.

No references cited. 

1. A PROCESS COMPRISING INTIMATELY AN AQUEOUS SLURRY CONTAINING (A) AN N-HIGHER ACYL TAURINE OF THE FORMULA R''CONR"-CHR-CHR-SO3M WHEREIN ONE R IS SELECTED FROM THE GROUP CONSISTING OF H AND METHYL AND THE OTHER R IS H, R" IS SELECTED FROM THE GROUP CONSISTING OF H, PHENYL, ALKYL RADICALS OF 1 TO 6 CARBON ATOMS, AND CYCLOHEXYL, R'' IS SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC AND ALICYCLIC HYDROCARBON RADICALS OF 7 TO 23 CARBON ATOMS, AND M IS SELECTED FROM THE GROUP CONSISTING OF H, ALKALI METAL, ALKALINE EARTH METAL, AMMONIUM AND AMINO, AND (B) A WATER SOLUBLE SALT SELECTED FROM THE GROUP CONSISTING OF THE ALKALI METAL CHLORIDES AND SULFATES, WITH A WATER INSOLUBLE COMPOUND (C) SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC AND ALICYCLIC MONOCARBOXYLIC ACIDS OF 8 TO 24 CARBON ATOMS AND THEIR ESTERS IN AN AMOUNT AND AT A TEMPERATURE SUFFICIENT TO FORM A COMPATIBLE LIQUID SOLVENT SYSTEM WITH SAID TAURINE (A), ALLOWING THE RESULTING MIXTURE TO SETTLE INTO A LOWER AQUEOUS PHASE ANS AN UPPER OIL PHASE CONTAINING SAID SOLVENT SYSTEM, AND THEN SEPARATING SAID AQUEOUS PHASE FROM SAID OIL PHASE AT A TEMPERATURE ABOVE THE SOLIDIFICATION POINT OF SAID SOLVENT SYSTEM. 